hree inches.

This constant ebb and flow of the great sea is a grand provision for
its purification. Even the wind is sent to the sea to be cleansed.
The sea washes every shore, purifies every cove, bay, and river
twice every twenty-four hours. All putrescible matter liable to
breed a pestilence is carried far from shore and sunk under fathoms
of the never-stagnant sea. The distant moon lends its mighty power
to carry the burdens of commerce. She takes all the loads that
can be floated on her flowing tides, and cheerfully carries them
in opposite directions in successive journeys.

It must be conceded that the profoundest study has not mastered
the whole philosophy of tides. There are certain facts which are
apparent, but for an explanation of their true theory such men as
Laplace, Newton, and Airy have labored in vain. There are plenty
of other worlds still to conquer.

[Page 150]
[Illustration: Fig. 57.--Lunar Day.]

[Page 151]
THE MOON.

New moon, [Symbol]; first quarter, [Symbol]; full moon, [Symbol];
last quarter, [Symbol].

EXTREME DISTANCE FROM THE EARTH, 259,600 MILES; LEAST, 221,000
MILES; MEAN, 240,000 MILES. DIAMETER, 2164.6 MILES [2153, LOCKYER].
REVOLUTION ABOUT THE EARTH, 29-1/2 DAYS. AXIAL REVOLUTION, SAME
TIME.

When the astronomer Herschel was observing the southern sky from
the Cape of Good Hope, the most clever hoax was perpetrated that
ever was palmed upon a credulous public. Some new and wonderful
instruments were carefully described as having been used by that
astronomer, whereby he was enabled to bring the moon so close that
he could see thereon trees, houses, animals, and men-like human
beings. He could even discern their movements, and gestures that
indicated a peaceful race. The extent of the hoax will be perceived
when it is stated that no telescope that we are now able to make
reveals the moon more clearly than it would appear to the naked
eye if it was one hundred or one hundred and fifty miles away.
The distance at which a man can be seen by the unaided eye varies
according to circumstances of position, background, light, and
eye, but it is much inside of five miles.

Since, however, the moon is our nearest neighbor, a member of our
own family in fact, it is a most interesting object of study.

A glance at its familiar face reveals its unequal illumination.
All ages and races have seen a man in the moon. All lovers have
sworn by its constancy, and only part of them have kep